The field of the present disclosure relates to systems and methods for item checkout and in certain aspects to retail checkstands or other checkout stands (e.g., a parcel distribution station) that incorporate data readers and other electronic devices. The field of the present disclosure further relates generally to data reading devices, and more particularly to automated devices by which items are conveyed, typically on a conveyor, through a read zone of the data reader by which the items are identified such as, for example, by reading optical codes or RFID (radio frequency identification) tags on the items.
Data reading devices are used to obtain data from optical codes or electronic tags (e.g., RFID tags), or use image recognition to identify an item. One common data reader device is an RFID reader. Another common data reader device is an optical code reader. Optical codes typically comprise a pattern of dark elements and light spaces. There are various types of optical codes, including linear or 1-D (one-dimensional) codes such as UPC and EAN/JAN barcodes, 2-D (two-dimensional codes) such as MaxiCode codes, or stacked codes such as PDF 417 codes. For convenience, some embodiments may be described herein with reference to capture of 1-D barcodes, but the embodiments may also be useful for other optical codes and symbols or objects.
Various types of optical code readers, also known as scanners, such as manual readers, semi-automatic readers and automated readers, are available to acquire and decode the information encoded in optical codes. In a manual reader (e.g., a hand-held type reader, a fixed-position reader), a human operator positions an object relative to the reader to read the optical code associated with the object. In a semi-automatic reader, either checker-assisted or self-checkout, objects are moved usually one at a time by the user into or through the read zone of the reader and the reader then reads the optical code on the object. In an automated reader (e.g., a portal or tunnel scanner), an object is automatically positioned (e.g., transported through the read zone via a conveyor) relative to the reader, with the reader automatically reading the optical code on the object.
One type of data reader is referred to as a flying spot scanner wherein an illumination beam is moved (i.e., scanned) across the barcode while a photodetector monitors the reflected or backscattered light. For example, the photodetector may generate a high voltage when a large amount of light scattered from the barcode impinges on the detector, as from a light space, and likewise may produce a low voltage when a small amount of light scattered from the barcode impinges on the photodetector, as from a dark bar. The illumination source in flying spot scanners is typically a coherent light source, such as a laser or laser diode, but may comprise a non-coherent light source such as a light emitting diode. A laser illumination source may offer advantages of higher intensity illumination which may allow barcodes to be read over a larger range of distances from the barcode scanner (large depth of field) and under a wider range of background illumination conditions.
Another type of data reader is an imaging reader that employs an imaging device or sensor array, such as a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) device. Imaging readers can be configured to read both 1-D and 2-D optical codes, as well as other types of optical codes or symbols and images of other items. When an imaging reader is used to read an optical code, an image of the optical code or portion thereof is focused onto a detector array. Though some imaging readers are capable of using ambient light illumination, an imaging reader typically utilizes a light source to illuminate the item being read to provide the required signal response in the imaging device. A camera is typically a combination of a lens and an imaging device/sensor array, but the terms imager and camera will be used somewhat interchangeably herein.
An imager-based reader utilizes a camera or imager to generate electronic image data, typically in digital form, of an optical code. The image data is then processed to find and decode the optical code. For example, virtual scan line techniques are known techniques for digitally processing an image containing an optical code by looking across an image along a plurality of lines, typically spaced apart and at various angles, somewhat similar to the scan pattern of a laser beam in a laser-based scanner.
Imager-based readers often can only form images from one perspective—usually that of a normal vector out of the face of the imager. Such imager-based readers therefore provide only a single point of view, which may limit the ability of the reader to recognize an optical code in certain circumstances. For example, because the scan or view volume of an imager in an imager-based reader is typically conical in shape, attempting to read a barcode or other image in close proximity to the scanning window (reading “on the window”) may be less effective than with a basket-type laser scanner. Also, when labels are oriented such that the illumination source is reflected directly into the imager, the imager may fail to read properly due to uniform reflection washing out the desired image entirely, or the imager may fail to read properly due to reflection from a textured specular surface washing out one or more elements. This effect may cause reading of shiny labels to be problematic at particular reflective angles. In addition, labels oriented at extreme acute angles relative to the imager may not be readable. Lastly, the label may be oriented on the opposite side of the package with respect to the camera view, causing the package to obstruct the camera from viewing the barcode.
Thus, better performance could result from taking images from multiple perspectives. A few imager-based readers that generate multiple perspectives are known. One such reader is disclosed in U.S. Pat. No. 7,398,927 which discloses an embodiment having two cameras to collect two images from two different perspectives for the purpose of mitigating specular reflection. U.S. Pat. No. 6,899,272 discloses one embodiment that utilizes two independent sensor arrays pointed in different orthogonal directions to collect image data from different sides of a package. Multiple-camera imager-based readers that employ spatially separated cameras require multiple circuit boards and/or mounting hardware and space for associated optical components which can increase the expense of the reader, complicate the physical design, and increase the size of the reader. Improved multi-camera systems are disclosed in U.S. Published Application Nos. US-2010-0163626, US US-2010-0163627, and US-2010-0163628.
The present inventors have, therefore, determined that it would be desirable to provide an improved imager-based reader and an improved tunnel or portal scanner system for automated checkout.